This invention relates in general to random access memory devices and, more particularly, to a normally volatile random access memory cell having non-volatile storage capability.
MNOS (metal-nitride-oxide-semiconductor) technology is currently being used successfully to produce monolithic integrated circuits having static or dynamic memories. The static memory cell can be formed in a non-volatile configuration. An example of a non-volatile static RAM memory cell is taught in U.S. Pat. No. 3,651,492 issued Nov. 2, 1970, to George C. Lockwood and assigned to the assignee of the present invention.
However, the prior art dynamic RAM cells are volatile and normally comprise an addressing transistor and a volatile storage capacitor. Memories based upon these calls usually have an emergency power source for maintaining data storage in the event that the primary power is lost. The volatile dynamic RAM has to be refreshed very frequently (on the order of every two milliseconds) and thus requires considerable energy for extended power down conditions. In such a situation, non-volatile operation is preferable to volatile operation.
As will be appreciated from the above, it is desirable to have a dynamic RAM memory cell which can be operated in a non-volatile mode.